Galileo’s “Letter” attempts to do several things at the same time: to define scientific practice, to defend the validity of his discoveries, and to show that his discoveries aren’t sacrilegious. Galileo does all three by defining each idea in terms of the other. He argues that you can’t commit heresy by exploring truth because God creates the truth. The Bible doesn’t explore every aspect of the natural world. Evidence-based research doesn’t contradict the Bible because the Bible works in metaphor, not in literal truth.

Galileo’s arguments rely on the same theme. Scientific observation and scriptural analysis serve different purposes and uncover different aspects of the universe. He argues that we need to consider what the Bible says concerning particular ideas in different places, explore different metaphorical possibilities, and discuss the questions that those possibilities raise.

Galileo also explains that we can’t apply the Bible to natural phenomena and expect it to provide exact results. The Bible uses metaphor, so its descriptions of the natural world don’t correspond to how the world operates. The Bible doesn’t try to correspond to the natural world at all. He writes, “I would say here something that was heard from an ecclesiastic of the most eminent degree: ‘That the intention of the Holy Ghost is to teach us how one goes to heaven, not how heaven goes’” (Paragraph 13).